Xylopiana A, a Dimeric Guaiane with a Case-Shaped Core from Xylopia vielana: Structural Elucidation and Biomimetic Conversion.

Xylopiana A (1), a dimeric guaiane with an unprecedented pentacyclo[5.2.1.01,2.04,5'.05,4']decane-3,2'-dione core, and three biosynthetically related intermediates, compounds 2-4, were isolated from the leaves of Xylopia vielana. Their structures and absolute configurations were determined by a combination of spectroscopic data, X-ray crystallography, electronic circular dichroism calculations, and chemical conversion. The structure of known vielanin A was revised to be compound 3. Compound 4 exerted a 3.7-fold potentiation effect on doxorubicin susceptibility at the tested concentration of 10 μM.